Private 

Water Crossings 

Considerations before you build or rebuild 

FEMA P-778 / June 2009 
PRIVATE	WATER	CROSSINGS 

Table Of Contents
	

1.	 Introduction	 1

2.		 Obtaining	a	Permit	 2

3.		 Water	Crossings	 3
 

3.1 Bridges . . . . . . . . . . . . . . . . . . 4
	

3.2 Culverts . . . . . . . . . . . . . . . . . 9
	

3.3 Low Water Crossings . . . . . . . . . . . . 13
	

4.	 Definitions		 15
	 PRIVATE	WATER	CROSSINGS	 |	 1 

1. Introduction
	

This	booklet	addresses	the	necessity	for	careful	

consideration	of	a	number	of	issues	to	gain	or	

regain,	and	to	maintain	safe	ingress	and	egress	over	

water	bodies	utilizing	private	crossings.

It	is	imperative	that	all	watercourse	crossings,	

including	bridges,	low	water	crossings	and	

culverts	be	properly	designed	and	constructed	

to	perform	safely	and	adequately	under	varying	

natural	conditions.	Any	watercourse	crossing	

has	the	potential	to	alter	or	disrupt	the	waterway	

characteristics	from	the	low	to	high	flow	

conditions.	Improper	installations	can	result	in	

extensive	loss	and	damage	to	public	and	private	

property,	danger	to	human	life,	as	well	as	damage	

to	the	environment	as	a	result	of	flooding,	erosion	

and	washouts.	Maintaining	the	overall	integrity	of	

the	waterway	is	of	the	utmost	importance.	

		

Construction	should	be	performed	during	dry	

weather	and	not	prolonged.		This	will	minimize	

risks	to	both	the	project	and	the	environment.		

Installation	should	not	be	done	in	frozen	ground.	

Structural	design	should	be	based	on	maximum	

anticipated	water	depth	and	velocity	in	addition	

to	the	intended	use	of	the	crossing.		Longer	and	

higher	bridges	are	often	more	economical	because	

they	will	sustain	less	damage	in	future	flood	events.

The	actual	design	and	installation	of	the	crossing	

needs	to	be	coordinated	with	all	persons	who	

may	be	involved	in	the	project:	owner,	engineer,	

contractor	and	governing	agencies	(local,	state	and	

federal).	

Because	each	land	and	water	site	is	unique,	and	the	

type	of	materials	and	the	quality	of	construction	

vary,	mechanisms	must	be	customized	to	each	

location.	It	is	not	possible	or	desirable	to	attempt	to	

address	all	considerations.	The	Federal	Emergency	

Management	Agency	(FEMA)	therefore	does	

not	warrant	the	completeness,	inclusiveness	or	

comprehensiveness	of	the	discussion	that	follows.

In selecting or evaluating a crossing site, some characteristics should be considered. 

The chosen location should be economical to both construct and maintain. 

Waterway crossing sites should be selected using the following criteria: 

• Fairly level and sufficiently long approaches with gentle slopes. 

• Firm and stable soil conditions. 

• Relatively shallow water depth and low velocity during floods. 

• Away from fish spawning areas, water intakes and lake outlet sites. 

• Minimum probability of scouring and sediment displacement. 

• Adequate space for entering the public highway at right angles. 
2	 |	 PRIVATE	WATER	CROSSINGS 

2. Obtaining a Permit
	

All	construction	of	waterway	crossings	require	

permits	from	at	least	one	if	not	multiple	local,	state	

and	federal	agencies	before	any	work	can	begin.	

Permits	may	also	be	required	for	any	or	all	of	

the	following:	Alterations,	enlargements,	repairs,	

maintenance	and	removal	of	bridges,	culverts	or	

low	water	crossings.	No	matter	where	you	live,	

there	exists	some	form	of	permitting	process	

required	for	any	watercourse	encroachment	or	

alteration.	Very	often	a	local	soil	conservation	

district	agency	works	along	with	the	United	

States	Army	Corps	of	Engineers,	Federal	and	State	

Clean	Water	Act	representatives,	Department	of	

Natural	Resources,	Environmental	Protection	

Agency,	United	States	Fish	and	Wildlife	Service,	

State	Division	of	Highways	and	a	local	Floodplain	

Administrator.		

Documentation	or	verification	should	be	given	

to	the	Floodplain	Manager	establishing	that	the	

flood	carrying	capacity	within	the	altered	area	

of	the	stream	in	question	will	be	maintained.		If	

hydrologic	and	hydraulic	analyses	are	required,	

qualified	personnel	shall	perform	them.

Building	techniques	that	may	be	required	to	present	

a	“best	practice”	in	the	construction	of	a	bridge,	

culvert	or	low	water	crossing	may	include:	Wing	

walls,	trash	grates	and	the	sizing	of	openings	to	

carry	anticipated	future	increases	in	flood	heights.		

The	design	or	redesign	and	the	actual	construction	

of	a	waterway	crossing	are	separate	parts	of	the	

total	project	often	handled	by	different	persons.	If	

so,	it	is	important	that	installation	procedures	are	

considered	during	the	design	phase	of	the	crossing.	

Communication	and	coordination	between	

designer,	builder	and	regulating	agencies	is	

necessary	to	achieve	a	quality-finished	product	with	

a	minimum	of	environmental	alterations	or	damage	

to	the	site.	A	minimal	amount	of	time	should	be	

spent	in	the	actual	water	channel.	

The	builder	usually	is	responsible	for	obtaining	

the	necessary	permits	and	ensuring	the	day-to-day	

construction	practices	follow	all	local,	state	and	

federal	regulations,	specifications	and	guidelines.	

Each	waterway	crossing	is	unique	and	requires	

well-planned	construction	methods.	

Failure	to	follow	the	local	permitting	process	and	

obtaining	approval	from	all	authorities	having	

jurisdiction	can	result	in	a	delay	of	your	installation	

or	an	order	to	stop	construction	and	formal	

enforcement	actions,	including	financial	penalties.		

artment of Natural Resources

Clear Span Bridge 

General Permit Packet 

(01/23/2008) page 1 of 8

General Permit

A General Permit is available for a clear span bridge under NR 320, Adm. Code. To qualify for this general permit, your project 

must meet eligibility standards. Designing your project to meet these standards helps conserve fish and wildlife habitat, water 

quality and other public rights which we all enjoy. In addition, this will help us make a prompt decision on your proposal. 

This application packet will allow you to supply the needed information for us to assure your project is eligible for a general 

permit. You will want to begin by gathering all the information contained in the checklist below. If your project is eligible, or 

meets all the criteria below, you should then fill out the general permit application and furnish that to the identified office for 

review. 

if you do not supply all the information contained in the eligibility requirements checklist or on the application, your 

project cannot be reviewed. after we receive your complete package, we will respond within 30 days to notify you that 

your project is eligible or that additional information is required to complete your application. In some cases, you may be 

notified that your project requires an individual permit.

WHat YOU neeD tO inClUDe WitH YOUr aPPliCatiOn:

note: To avoid delays, supply all of the information listed below in a complete and organized

format. Detailed descriptions of the necessary information and common mistak

in our Permit Partner Document.

q Photographs showing 

waterb
	 PRIVATE	WATER	CROSSINGS	 |	 3 

3. Water Crossings 

This	booklet	places	crossings	in	three	categories:	 Watercourse	crossings	should	be	appropriately	
 

bridges,	culverts	and	low	water	crossings.	Specific	 designed	to	minimize	the	disturbance	of	
 

information	about	each	follows.	 streambeds	and	flow	velocities.	
 


 

If designed and constructed properly, 

bridges are preferred to culverts and low 

water crossings, since the latter two can 

alter the natural flow of the water. 

WHEN 

FLOODED 

TURN AROUND 

DON’T 

DROWN 
4	 |	 PRIVATE	WATER	CROSSINGS 

3.1 Bridges 

Quality	designed	and	constructed	bridges	can	

maintain	the	original	watercourse	channel	bed	

without	any	alteration	or	disturbance.		Some	

types	of	structures	tend	to	restrict	and	obstruct	the	

normal	and	above	normal	flow	of	the	waterway.		

Clear-span	bridges	do	not	require	infilling	or	

restrict	the	area	of	water	flow	as	culverts	or	multispan	bridges	do.

Bridges	provide	better	capacity	to	accommodate	

high	flows	while	creating	better	inlet	and	outlet	

conditions	that	allow	debris	to	pass	through	

without	blockage.		

Flood	damage	to	bridges	includes	floodwaters	

overwhelming	the	deck	and	superstructure	as	a	

result	of	inadequate	attention	paid	to	the	hydraulic	

capacity	of	the	bridge.	Damage	also	results	from	

impact	and	accumulation	of	debris.	

SALVAGE ANY 

TREES AND 

SHRUBS 

WATER CHANNEL 

SHOULD BE LEFT 

UNDISTURBED 

RIPRAP INSTALLED 

UNDER BRIDGE AND 

ALONG BANKS TO 

STABILIZE AREA IF THE 

ESTABLISHMENT OF 

VEGETATION OR FILTER 

FABRIC IS NOT 

APPLICABLE. 

BRIDGE DRIVEWAY OR LANE 

GUARDRAIL 

WINGWALL 

BANK STABILIZATION AT ALL FOUR 

BRIDGE QUADRANTS SEED AND 

MULCH OR SOD 

WATER 

FLOW 

Figure 3.1-1. Plan view of bridge
	
	 PRIVATE	WATER	CROSSINGS	 |	 5
 

Design consideration for bridges: 

•	 Span	the	entire	water	channel	without	altering	the	water	banks	or	bed	and	having	the	abutments	

or	piers	encroaching	into	the	channel.

•	 Adequately	handle	storm	water	runoff	from	the	roadway.	

•	 Utilize	a	“perched”	bridge	design	with	low	roadway	approaches	to	sacrifice	the	roadway	and	save	

the	bridge	under	severe	flood	conditions.

•	 Install	wing	walls	to	direct	the	water	flow	into	the	bridge	opening	to	eliminate	potential	erosion.

•	 Avoid	the	direct	contact	of	uncured	concrete	and	pentachlorophenol	-	treated	wood	with	the	

water	to	avoid	the	toxic	reaction	to	aquatic	life.	

•	 Handrails	or	guardrails	should	be	installed	where	necessary.

•	 Stabilize	the	disturbed	areas	with	native	vegetation	whenever	possible	versus	using	structural	

solutions:	bulkheads,	riprap	and	other	structural	solutions.

Figure 3.1-2. Concrete is being 

poured into a wood form for a 

cast in place reinforced concrete 

bridge abutment with wing walls. 

This abutment design was dictated 

by a short approach, but it is 

still high and set back far enough 

from the water channel to allow 

unobstructed water flow and safe 

passage to and from the property. 

Figure 3.1-3. Bridge with wing 

walls direct water flow during high 

water to avoid washout of bridge 

approach and increase of water 

flow velocity. Guardrails on bridge 

safeguard traffic passage. 
6	 |	 PRIVATE	WATER	CROSSINGS 

Figure 3.1-4. This bridge design 

was dictated by exposed bedrock. 

Site-specific conditions and good 

judgement resulted in safe traffic 

passage and a practical approach 

to stream protection. Even during 

high water, this bridge should 

maintain appropriate flow and 

streambed and not constrict the 

stream. 

Figure 3.1-5. Private bridge 

with secured handrails and 

unobstructed water flow allows 

for safe traffic passage and creates 

no noticeable change in the 

stream flow or streambed. The 

bridge crossing is wide and high 

relative to its length. 

Figure 3.1-6. Perched bridge 

and low water crossing. The low 

water crossing is used only for 

infrequent passage by heavy farm 

equipment. The perched bridge is 

for regular access to property, but 

can become an island during a 

flood if the road on both sides is 

under water. 
	 PRIVATE	WATER	CROSSINGS	 |	 7 

Bridge Crossing Problems
	

Figure 3.1-7. A bridge pier 

located in the water channel creates 

scouring and debris catch which 

exacerbates the impact of flooding. 

Routine maintenance is required to 

prevent accumulation of debris. 

Figure 3.1-8. Bridge abutments 

encroaching into the stream creates 

a weakening of the structural 

integrity of the crossing during 

high water flow by erosion and 

scouring. 

Figure 3.1-9. The lack of wing 

walls and a short bridge span 

causes loss of bridge approach 

during high water. A longer bridge 

span with abutments set back from 

the water channel utilizing wing 

walls would avoid scouring and 

erosion. 
8	 |	 PRIVATE	WATER	CROSSINGS 

The	bridge	design	below	has	been	successfully	used

where	the	stream	banks	are	firm	enough	to	prevent	

erosion	and	support	the	abutments.		No	concrete	

is	needed.		The	stringers	are	welded	to	the	steel	

abutment	members	that	sit	directly	on	the	soil.	

Appropriately	designed	bridge	foundation	can	also	

be	gabion	abutment,	footings	or	logs	set	into	rock	

or	firm	stable	soil.

STEEL ANGLE 

TO SUPPORT 

DECK LUMBER 

BACKFILL 

WITH STONE 

GALVANIZED 

STEEL PLATE 

TIMBER 

DECK 

Figure 3.1-10. Side elevation section view of private bridge without concrete abutments 

The	deck	slab	or	stringers	should	be	set	above	the	

expected	high	water	level	to	allow	for	debris	and	

storm	flow	passage.	Add	protection	against	sour,	

such	as	riprap,	gabions	or	vegetation.

Figure 3.1-11. Perspective and section view of private bridge without concrete abutments 

STEEL 

ABUTMENT 

MEMBER 

TIMBER 

CURB 

GALVANIZED STEEL PLATE 

(WELD OVER “I” BEAM 

STRINGERS 

AND ABUTMENT MEMBER 

BACKFILL WITH 

STONE 

TIMBER 

DECK 

STEEL 

STRINGERS 

ANGLE 

IRON 
	 PRIVATE	WATER	CROSSINGS	 |	 9 

3.2 Culverts 

	life	

be

Culverts	can	be	used	for	a	watercourse	crossing	where	

the	installation	of	a	bridge	is	not	feasible	and	

the	impact	on	fish	and	other	aquatic

is	minimal.		Culverts	are	appropriately

used	 for	 access	 across	 drainage

ditches,	 intermittent	 streams	

and	 small	 waterways.	 Culverts	

often	 fail	 to	 accommodate	

high	 water	 flows.	 This	 results	

in	 washouts,	 erosion	 and	 flow	

blockage	 by	 debris	 buildup.	

Commonly	available	culverts	are	

made	of	corrugated	steel,	polyethylene	

or	reinforced	concrete.		Multiple	culverts	are	

not	recommended	due	to	the	trapping	of	debris.		

If	a	waterway	is	too	wide	or	large	for	a	

single	culvert,	then	the	design	should	

	changed	to	a	bridge.		To	correctly	

install	a	multiple	or	‘gang’	culvert	

crossing,	a	thorough	hydraulic	

and	hydrologic	analysis	is	

needed.	A	minimum	distance	is	

needed	between	culverts	with	

infill	to	be	properly	compacted.	

This	fill	must	be	protected	from	

washing	out	by	installing	an	end	

wall	or	armoring	at	the	inlet	and	

outlet	areas.		A	debris	guard	could	also	

be	needed.

Figure 3.2-1. Culvert in section 

EXISTING 

GROUND 

ROCK FREE 

CULVERT BED 

(GRAVEL OR SOIL) 

TAMP BACKFILL 

MATERIAL AT 

REGULAR INTERVALS 

CULVERT 

LEVEL OF 

NATURAL 

STREAMBED 

BASE AND SIDEWALL 

FILL MATERIAL SHOULD 

BE FINER SOIL 

PARTICLES COMPACTED 

ONE FOOT MINIMUM OR 

ONE THIRD OF TOTAL 

DIAMETER FOR LARGE 

CULVERT 

ROAD SURFACE 

The	culvert	must	have	a	large	enough	opening	to	

handle	peak	runoff.	Ideally,	a	properly	designed	

culvert’s	simulated	bed	will	reflect	the	natural	

streambed	where	water	flow	conditions	inside	

the	culvert	are	much	like	the	conditions	at	the	

upstream	and	downstream	sites	of	the	crossing.
10	 |	 PRIVATE	WATER	CROSSINGS 

Figure 3.2-2. This multiple 

culvert crossing is vulnerable to 

debris blockage and washout. 

To install multiple or a “gang” 

of culverts properly, each culvert 

must be spaced adequately to 

allow for proper soil compaction 

between the culverts. This fill 

must be well armored at each 

end to prevent the washing out 

between the culverts. 

Figure 3.2-3. (right) Insufficient cover for culverts will 

result in washout and erosion as well as structural failure and 

collapse of culverts. 

Design considerations for culverts:

•	 The	culvert	must	provide	for	proper	road	width	and	side	slopes.

•	 Wing	walls	may	be	used	to	aid	in	directing	the	flow	of	water	at	the	outlet	and	directly	into	the	

inlet	to	help	prevent	erosion.

•	 Headwalls	may	prevent	washouts	at	steep	slopes	and	unstable	fill	sites.

•	 Culvert	should	be	installed	so	that	the	existing	waterway	slope/gradient	is	not	changed.	

•	 The	culvert	should	be	aligned	with	the	waterway,	with	no	changes	in	water	flow	direction	at	the	

upstream	or	downstream	area	of	the	crossing.	

•	 Culverts	should	never	be	installed	with	bends	in	them.	

•	 Recess	the	bottom	of	the	culvert	to	a	depth	at	least	12	inches	below	the	existing	streambed	or	to	

the	projected	scour	depth	of	the	natural	channel.		

•	 When	a	debris	barrier/trash	grate	is	used	to	catch	debris,	the	grate	should	be	installed	with	a	

low	incline	to	prevent	floating	debris	from	being	held	against	the	grate	by	the	flow.	This	can	

cause	washouts.	

•	 Culverts	should	be	inspected	after	heavy	rainstorms	and	flood	events.	

•	 Height	restrictions	may	require	the	use	of	a	horizontally	elongated	culvert,	which	result	in	

better	low	flow	characteristics.	
	 PRIVATE	WA CROSSINGS	 |	 TER	 11
 

•	 Cast-in-place	or	self-setting	concrete	bag	headwalls	

exposed	to	the	watercourse	are	less	desirable	than	precast	concrete	or	sandbagged	headwalls,	due	to	the	release	

of	leachate	and	resulting	fish	kill.

•	 Sandbagged	headwalls	are	traditionally	used	as	a	temporary	

measure	and	for	sandy	non-clay	soil	conditions.

•	 Adequately	designed	and	constructed	bottomless	arch	culverts	

can	maintain	natural	streambed	and	match	the	upstream	and	

downstream	water	depth	and	velocity.

Figure 3.2-4. Culvert with 

sandbagged headwall is being

used in a sandy soil drainage 

ditch. This method should no

be used for permanent use in 

water courses. 

Figure 3.2-5. Multiple 

culverts at driveway ditch 

crossing have adequate spacing 

and compaction. The concrete 

headwall and wing walls help 

direct water flow and prevent 

washouts during high water 

flow. There is also adequate 

cover and culvert length to 

allow liberal clearance of 

traffic. 

t 
12	 |	 PRIVATE	WATER	CROSSINGS 

Figure 3.2-6. This headwall at a 

culvert inlet protects against erosion 

and washout. Many inlet failures 

occur on culverts without headwalls 

or other entrance protection. When 

soils adjacent to the inlet are eroded 

or become saturated, pipe inlets 

can be subjected to buoyant forces 

causing culverts to dislodge and 

washout. 

Figure 3.2-7. Culvert aligned 

with stream and armored with 

stone at inlet and outlet. Natural 

streambed conditions preserved 

by embedding culvert, allowing 

water to flow naturally without 

undercutting the inlet and causing 

erosion. 

Figure 3.2-8. These culvert wing 

walls aid in directing water flow. 

The mitered or skewed ends of 

corrugated metal pipes, cut to 

conform to the embankment slopes, 

offer little resistance to bending or 

buckling without wing walls. Wing 

walls help prevent scouring and 

protect embankment slopes. 
	 PRIVATE	WATER	CROSSINGS	 |	 13 

3.3 Low Water Crossings 

Low	water	crossings	have	limited	application	due	

to	continued	disturbance	of	the	streambed	and	

frequent	inundation.		Do	not	use	a	low	water	

crossing	to	serve	occupied	dwellings	where	no	

alternate	emergency	access	is	available.	They	are	

more	suitable	for	low	volume	roads	with	no	

habitable	dwellings	where	the	normal	volume	of	

water	flow	is	relatively	low.	

Low	water	crossings	can	be	useful	for	infrequently	

crossed	waterways	that	experience	

flash	floods,	since	it	would	be	

uneconomical	to	construct	a	bridge	

or	culvert.		Debris	problems	and	

other	maintenance	are	minimized.		

Proper	signs	should	be	used	

warning	of	the	dangers	of	high	water.

IMPASSABLE 

DURING 

HIGH WATER 

The	more	stable	the	streambed	and	banks	are	with	

bedrock,	and	the	lower	the	existing	bank	slopes	and	

grades	are,	the	more	suitable	the	site	is	for	a	low	

water	crossing.	Approach	grades	should	be	less	than	

10%.		Sites	that	consist	mostly	of	sand	and/or	silt	

are	not	appropriate	for	fording/crossing.

Two	types	of	low	water	crossings	are	the	unvented	

ford	and	the	vented	ford.

Unvented	fords	are	constructed	of	riprap,	gabions,	

or	concrete	to	provide	a	stream	crossing	without	

the	use	of	pipes	where	streams	are	dry	most	of	the	

year	and	crossing	use	is	temporary.	Water	depth	

flow	over	an	unvented	ford	should	not	exceed	6	

inches.

Vented	fords	use	pipes	under	the	crossing	to	allow	

low	flows	to	pass	through	without	regularly	passing	

over	the	crossing.	The	pipes	or	small	culverts	may	

be	placed	in	aggregate,	riprap,	gabions	or	concrete.

Figure 3.3-2. Concrete vented ford - this type of crossing has a 

low cost and low maintenance. Fish passage and scouring problems 

are a disadvantage as well as a danger to traffic during high flow 

periods. 

Figure 3.3-1. Low water crossing - this can be suitable for very 

low-volume access. Unimproved ford is a natural crossing that is 

undesirable for daily use. 
14	 |	 PRIVATE	WATER	CROSSINGS 

A	box	culvert	is	a	crossing	design	that	is	used	

more	frequently	in	areas	where	habitat	protection	

is	important.	A	single	or	series	of	box	culverts	are	

embedded	with	continuous	streambed	material	

through	the	structure.	These	structures	perform	like

a	bridge	by	matching	the	channel	width.	

It	is	important	that	any	washout	of	streambed	

material	during	high	water	flow	is	refilled	naturally	

with	sediment	as	flow	recedes.

Figure 3.3-3. Embedded box culverts 

ANTI-SCOUR 

DOWNSTREAM 

CUTOFF WALL 

(TYPICALLY 3’ - 5’ 

DEEP) 

EMBEDDED BOX 

CULVERTS SET 

BELOW CHANNEL 

LEVEL 12”-24” TO 

FORM A “NATURAL” 

STREAM BOTTOM 

NATURAL CHANNEL 

PROFILE 

BANKFULL WIDTH ROAD SURFACE 

Embedded	box	culverts	maintain	a	continuous	

streambed	through	the	structure.	If	site	conditions	

permit,	an	open-bottom	box	with	a	natural	stream	

channel	bottom	is	preferable	in	sustaining	channel	

function.

Figure 3.3-4. Concrete vented ford - The number of box openings depends upon the width and flow of the channel. A continuous 

streambed maintains channel function. 
PRIVATE	WATER	CROSSINGS	 |	 15 

4. Definitions
	

Abutment:	Part	of	a	structure	which	supports	

the	end	of	a	span;	often	supports	and	retains	the	

approach	embankment.

Aquatic Life:	All	forms	of	living	things	found	in	

water,	ranging	from	bacteria	to	fish	and	rooted	

plants.	Insect	larva	and	zooplankton	are	also	

included.

Armoring:	A	facing	layer	(protective	cover),	

or	riprap,	consisting	of	very	large	stones	placed	

to	prevent	erosion	or	the	sloughing	off	of	an	

embankment.		

Best Practice:	The	optimum	construction	method	

put	into	practice	at	a	particular	place	and	time.	

Bridge:	A	watercourse	crossing	that	can	maintain	

the	original	natural	watercourse	channel	bed	

without	any	alteration	or	disturbance.	This	crossing	

structure	is	built	so	that	people	can	get	from	one	

side	to	the	other.	

Cast-in-place concrete:		Concrete	in	an	

unhardened	state,	primarily	as	ready-mix	and	

poured	in	forms	to	harden	on-site.	

Clear-span:		Bridge	structures	that	completely	span	

a	watercourse	and	do	not	encroach	on	the	natural	

channel	width	by	the	placement	of	abutments,	

footings	or	armoring	so	that	there	is	no	restriction	

to	the	natural	channel	processes.

Conduit:	Any	pipe,	tube,	or	drain	tile	through	

which	water	is	conveyed.	

Conveyance:	Floodwater	carrying	capacity	in	a	

passage	area	of	a	watercourse.	

Culvert:	A	drain,	pipe	or	channel	which	allows	

water	to	pass	under	a	road	or	embankment.

Debris:	Any	material	including	floating	woody	

materials	and	other	trash,	suspended	sediment	or	

bed	load	moved	by	a	flowing	stream.	

Deck:	The	top	surface	of	a	bridge	which	carries	the	

traffic.

Embankment:	Angled	grading	of	the	ground.

Filter fabric:	Geotextile	erosion	fabric	used	to	

cover	and	stabilize	topsoil	for	use	with	riprap	and	

ground	cover.	

Floodwaters:	Water	flows	that	have	risen	above	the	

stream	bank	and	flow	over	adjoining	lands.	

Gabion:	A	galvanized	wire	box	filled	with	stones/

riprap	used	to	form	an	abutment	or	retaining	wall.

Headwall:	A	wall	at	the	end	of	a	drainage	structure	

designed	to	prevent	erosion	of	the	embankment	at	

its	entrance	or	outlet.	

Infilling:	Soil,	rock,	gravel	or	a	combination	placed	

in	a	depression	or	ditch	to	fill	the	void.	Used	in	

conjunction	with	a	culvert.	

Low water crossing:	A	fording	site	of	a	waterway.	

Multi-span bridge:	Multiple	horizontal	spaces	

between	two	abutment	supports,	with	one	or	more	

piers	at	a	location	between	abutments.

Perched bridge:	Style	of	bridge	elevated	or	raised	

at	both	ends	to	avoid	floodwaters	and	create	low	

roadway	approaches.	The	bridge	is	higher	than	the	

floodplain,	but	the	approaches	are	much	lower.

Pier:	A	vertical	structure	(column	or	pile),	which	

supports	the	ends	of	a	multi-span	superstructure	at	

a	location	between	abutments.		
16	 |	 PRIVATE	WATER	CROSSINGS 

Piping:	Washing	out	or	erosion	between	and	

around	culverts.	

Pre-cast concrete:	Concrete	components	which	are	

cast	and	partly	matured	in	a	factory	or	on	the	site	

before	being	lifted	into	their	final	position	as	part	

of	a	structure.

Riprap:	Rock	placed	on	embankment	slopes	to	

prevent	erosion.		

Sediment:	Stone,	gravel	or	cobbles	that	originate	

from	the	weathering	of	rocks	and	is	transported	by,	

suspended	in,	or	deposited	by	water.	

Scour:	The	result	of	an	erosive	action	of	flowing	

water	in	waterways,	excavating	and	carrying	away	

material	from	the	bed	and	banks.	

Span:	The	horizontal	space	between	two	supports	

of	a	structure.	Also	refers	to	the	structure	itself.

Trash Grate: A	debris	guard	or	screen	placed	at	the	

upstream	entrance	of	a	culvert,	which	stops	heavy	

floating	debris	away	from	the	culvert	entrance	

during	high	velocity	flow.	

Watercourse:	Any	natural	or	artificial	channel	

through	which	water	flows;	a	lake,	river,	creek,	

stream,	wash,	arroyo,	channel	or	other	topographic	

feature	on	or	over	which	waters	flow	at	least	

periodically.

Wing wall:	Side	extensions	of	a	retaining	wall	as	

part	of	an	abutment;	used	to	contain	the	fill	of	an	

approach	embankment	and	to	direct	and	confine	

the	flow.
U. S. DEPARTMENT OF

HOMELAND SECURITY

FEMA
 FEMA P­778

Catalog No. 09301­2